1. Field of the Disclosure
Embodiments disclosed herein generally relate to methods to determine a fluid type of a fractured formation within a wellbore. More specifically, embodiments disclosed herein relate to methods using an induction tool when determining a formation type within a wellbore.
2. Background Art
Wells are generally drilled into the ground to recover natural deposits of hydrocarbons and other desirable materials trapped in geological formations in the Earth's crust. A well is typically drilled using a drill bit attached to the lower end of a drill string. The well is drilled so that it penetrates the subsurface formations containing the trapped materials and the materials can be recovered.
The drilling operations are controlled by an operator at the surface. The drill string is rotated at a desired rate by a rotary table, or top drive, at the surface, and the operator controls the weight-on-bit and other operating parameters of the drilling process. At the bottom end of the drill string is a “bottom hole assembly” (“BHA”). The BHA includes the drill bit along with sensors, control mechanisms, and the required circuitry. A typical BHA includes sensors that measure various properties of the formation and of the fluid that is contained in the formation, as well as the operating conditions of the drill bit and other downhole equipment.
Another aspect of drilling and well control relates to the drilling fluid, generally called “mud.” The mud is a fluid that is pumped from the surface to the drill bit by way of the drill string. The mud may serve to cool and lubricate the drill bit and then carry the drill cuttings back to the surface. The density of the mud is carefully controlled to maintain the hydrostatic pressure in the borehole at desired levels.
After drilling and developing the wellbore, the formation then may be prepared for production. During production, the wellbore may produce both hydrocarbons, such as gas and oil, in addition to water. Generally, the formation and wellbore will continue to be produced for as long as is economically efficient. When the wellbore then is no longer economically efficient, such as when the wellbore is no longer producing hydrocarbons, or is only producing small amounts of hydrocarbons as compared to water, the wellbore may then be abandoned or worked-over.
Workover of a wellbore refers to the repair or stimulation of an existing wellbore for the purposes of restoring, prolonging, or enhancing the production of hydrocarbons from a wellbore. For example, a wellbore may be producing excessive water, thereby preventing the wellbore from being economically efficient. The wellbore may be worked-over to restrict the water production of the wellbore and then continue or stimulate hydrocarbon production. This may be done by sending a measuring tool downhole to determine the various fluid types in the fractures within the wellbore (e.g., a water-filled fracture and a hydrocarbon-filled fracture), in which the fluid type in the fracture may be different from the fluid type within the matrix of a formation.
A fractured formation generally includes two parts: 1) a low porosity, low permeability matrix (i.e., formation), and 2) a network of high permeability fractures, such as naturally occurring or induced fractured reservoirs, that may act as conduits for fluid flow. As is common, the measuring tools used downhole to characterize a fractured formation are usually shallow probing log tools, such as an Oil-Based Micro-Imager (“OBMI”) tool or a Formation Micro-Imager (“FMI”). These shallow probing log tools usually can only measure the properties of the formation type with only a few inches (e.g., ˜3.5 in or 8.9 cm) for depth-of-investigation (“DOI”). DOI refers to the distance that characterizes how far a tool measures into the formation from the face of the measuring tool or the borehole wall. Because this DOI of the measuring tools is so shallow, and because drilling fluids may be pumped downhole, the measuring tools may not accurately measure the fluid type within the fractures, in addition to determining if the fractures are closed (e.g., healed), partially-closed, or open. Accordingly, there exists a need to more accurately measure the fluid types in the fractures of a fractured formation and to characterize the closure/openness of the fractures to determine if it may be appropriate to produce or workover the wellbore.